1. Field of the Invention
The present invention relates to a bronze-based sintered contact component and a method of making the same. The component is applicable for use in the art of contact components, such as friction devices of clutches and brakes for use under dry conditions or clutches for use under wet conditions incorporated in automatic transmissions, because it has exceptional resistance to wear and fusion, can stably retain a comparatively high coefficient of friction, is very unlikely to attack counterpart material, and further has high strength, high toughness, and high hardness.
2. Description of the Prior Art
Recently, for use as materials for friction clutches and brakes to be used under dry conditions, bronze-based sintered alloys have been developed which can replace asbestos-based friction materials. For example, Japanese Patent Application Laid-Open No. 58-126948 describes a "dry sintered friction material" which comprises a bronze-based sintered alloy and hard particulate matter added thereto to provide higher coefficient of friction.
However, such sintered material has no reaction layer between the hard particulate matter dispersed in the alloy and the matrix, but involves gaps therebetween. As such, during friction contact under high-speed, high-load contact conditions, hard particles may come off the matrix, and this makes it impracticable to expect any high friction coefficient to be stably exhibited. Another problem is that fusion may occur relative to counterpart material starting from the point at which such particle fall-off has occurred. Further, the sintered material involves problems, such as bite of come-off particles and attack against counterpart material. Additionally, in the aspect of mechanical characteristics, the sintered material as an abrasion material involves the problem that aforesaid gaps will deteriorate the mechanical characteristics of the material, such as strength, toughness and hardness. Another problem is that the dispersed hard particles are diametrically large-sized on the order of 30 to 80 .mu.m, which fact, as a source of fracture, will induce deterioration in strength and toughness.
The present inventors succeeded in uniformly dispersing various kinds of hard particles in a Cu-Sn based alloy powder or mixed powder as a matrix by mechanically alloying the former with the latter. As a result, they filed a Japanese patent application on a sintered friction material having both friction contact characteristics and mechanical characteristics under dry conditions, serially numbered as Japanese Patent Application No. 4-317756, entitled "Sintered Friction Material". Generally, prior art friction materials, including this friction material, are used together with a reinforcing plate of copper, cast iron, or stainless steel make to which the friction material is bonded. That is, from the view point of strength and toughness, it has been found impracticable to use such friction material alone in such application as structural components.
Also, for use as friction materials to be used under wet environments such as lubricating oils, primarily paper-make friction materials or carbon sintered materials have been developed. As an example of the former, Japanese Patent Application Laid-Open No. 6-25653 proposes a "paper friction material," which is a friction material containing a thermosetting resin such as phenol resin and a friction controller such as graphite powder or organic dusts as its main components, and organic fibers or carbon fibers as its reinforcing material. As an example of the latter, on the other hand, Japanese Patent Application Laid-Open No. 4-76086 proposes a "wet type friction material," which is a carbon fiber reinforced carbon sintered material obtained by sintering a complex composed of uncarbonated carbonaceous fibers and carbonaceous powder.
Both of the aforementioned materials are designed for use as friction materials to be used in automatic transmissions of automobiles. However, they show small coefficients of friction in oil as low as 0.1 to 0.15. Moreover, the paper-make friction materials lack in heat resistance so as to be worn and damaged during frictional contact under high temperatures and to deteriorate in characteristics. As a result, their coefficient of friction may lower, disadvantageously.